1. Field of the Invention
The present invention relates to a digital camera and a camera system having an automatic focusing (AF) control function.
2. Description of the Related Art
Heretofore, as an AF mechanism disposed in a single-lens reflex camera using a film and a single-lens reflex digital camera, a through-the-lens (TTL) phase-difference AF mechanism has been frequently used. In this case, a defocus detection mechanism which performs the TTL phase-difference AF is disposed in a main body of the single-lens reflex camera. Moreover, a focusing lens disposed in a lens barrel of an interchangeable lens which is detachably attached to the single-lens reflex cameras is driven by a motor disposed in the lens barrel of the interchangeable lens or the main body of the single-lens reflex camera to perform a focusing control operation. It is to be noted that the TTL phase-difference AF is sometimes referred to simply as the phase-difference AF.
On the other hand, in a compact digital camera, a camcorder or the like, so-called imager AF is frequently performed which is AF of such a system that contrast is detected with a high frequency component of a signal of an image pickup device. Here, the imager AF is an auto focusing method where an evaluated focal value of a focus lens at each focus lens position is calculated while moving the focus lens at a predetermined driving amount interval, and the focus lens position where the evaluated focal value reaches a peak value is obtained.
It is to be noted that the TTL phase-difference AF and the imager AF have the following characteristics, respectively.
The TTL phase-difference AF is the AF at a speed higher than that of the imager AF.
The imager AF is the AF having a precision higher than that of the TTL phase-difference AF.
Based on such characteristics, the TTL phase-difference AF and the imager AF are selectively used in accordance with an application. Here, as a technology in selectively using the TTL phase-difference AF and the imager AF, for example, the following technology is known.
In Japanese Patent Application Laid-Open No. 7-43605, an automatic focusing device is disclosed in which the TTL phase-difference AF is combined with the imager AF to perform focusing control. Specifically, in this automatic focusing device, after coarse control is performed by the TTL phase-difference AF, fine control is performed by the imager AF.
Moreover, in Japanese Patent Application Laid-Open No. 2003-302571, an automatic focusing control device is also disclosed in which after the coarse control is performed by the TTL phase-difference AF, the fine control is performed by the imager AF in the same manner as in the automatic focusing device disclosed in Japanese Patent Application Laid-Open No. 7-43605. However, in this automatic focusing control device disclosed in Japanese Patent Application Laid-Open No. 2003-302571, to speed us the focusing, the TTL phase-difference AF is selected in preference to the imager AF, when it is decided that the focusing is possible with the TTL phase-difference AF alone.
In addition, for a lens-interchangeable single-lens reflex camera using a film, many interchangeable lenses are on sale and already spread widely. Here, many of the interchangeable lenses which have already spread are designed to perform the TTL phase-difference AF. That is, focusing control mechanisms and the like of the focus lenses disposed in the lens barrels of many interchangeable lenses are designed as a system which drives the lens by a driving amount corresponding to a detected defocus amount. Specifically, as a driving source for the focusing control in the interchangeable lens barrel, a direct-current motor (a DC motor) is employed in many cases. On the other hand, as the driving source of the focus lens in the imager AF, a stepping motor is optimum. In actual, stepping motors are employed in many cases of the imager AF.